AMAROOSA RANGE, IGNEOUS ROCKS. 
microscopic examination, to be latite, and the series probably includes 
latite and siliceous dacite in addition to rhyolite. Compact aphanitic 
red fades of rhyolite are also common, and in these flow banding 
lithophysa?, and spherulites are well developed. The rhvolite of 
Shale Peak (elevation, 7,370 feet), 4 miles southeast of Wahguvhe 
Peak, is a faded brick-red rock banded with pink lines. Exfoliation 
breaks this rock, which is rather poor in phenocrysts, along the flow 
lines into numberless platy fragments, which caused the members of 
a United States Coast and Geodetic Survey party to give the peak 
its expressive name. Many angular inclusions of rhyolite of 
slightly different character occur in the lava, forming flow breccias. 
The rhyolite is in some places kaolinized and in others silicified. 
(See p. 47.) It is probable that much of the rhyolite that is now, 
through kaolinization, white or light gray in color, was formerly 
brick-red, since at certain places bleaching has occu Ted along joint 
fractures and irregular cracks, forming mottled fantastic patterns 
in reds and whites. 
Beds and lenses of red, white, and greenish-white incoherent sandy 
rhyolitic tuff's, containing feldspar, quartz, and biotite crystals, are 
interbedded with the lavas. In these tuffs pebbles of rhyolite, which 
in rare instances reach a diameter of 1 foot, are abundant. All 
gradations exist between the normal igneous rock and these sedi- 
ments deposited in small lakes or subaerial basins. 
The earlier rhyolite of the Amargosa Range occurs in flows from 
10 to 300 feet thick, superimposed one upon another, which impart 
to the eastern side of the range its varicolored banding. The thick- 
ness of the series is unknown, although it reaches at least 3,000 feet. 
The greater portion outflowed as lava, but at various times during the 
extrusion rhyolitic material was deposited in local sheets of water 
and at others dust from explosive eruptions formed subaerial accu- 
mulations. The vents from which the rhyolite flowed are probably 
situated near the crest line, but their position was not determined 
in the course of the present work. Where the rhyolite flows vary 
considerably in hardness the more resistant beds form benehes and 
the softer beds are covered by talus, a method of weathering well 
developed on the eastern side of the north end of the range. Where 
vertical systems of joints are prominently developed, outcrops are 
bounded by vertical planes and rock pinnacles form. If the rhyolite 
flows are of approximately equal hardness and joints are not promi- 
nent, rounded bosses and smooth domelike hills result. Such forms 
are well seen near Shale Peak. Perhaps the most common topo- 
graphic forms are cones, a mean between the pinnacles of the well- 
jointed rhyolite and the domelike hills of the more massive facies. 
The earlier rhyolite lies upon the eroded surface of the Paleozoic 
rocks and the biotite andesite and near contacts contains numerou 
